Reversible sprag clutch

ABSTRACT

A reversible sprag clutch has a plurality of sprags disposed between spaced, opposed circular surfaces of two concentric members forming races for convex-convex contact wherein each of the sprags has two distinct inner cam surfaces, one of which inner cam surfaces can be employed to prevent relative clockwise rotation between the concentric members and the other of which inner cam surfaces can be employed to prevent counterclockwise rotation of the concentric members. These sprags are so constructed that the clutch transmitting torque in one direction will allow unrestricted rotation in the opposite direction depending upon which of the inner cam surface is cooperating with the inner race. Through the use of a selector ring to bias the individual sprags, it is possible to selectively reverse the direction of torque transmission to the clutch and allow &#39;&#39;&#39;&#39;freewheeling&#39;&#39;&#39;&#39; in the opposite direction.

' United States Patent [72] Inventor David N. Sederquist 2727 #3 MidtownCourt, Palo Alto, Calif. 94303 [21] Appl. No. 41,419 [22] Filed May 28,1970 [45] Patented Aug. 17, 1971 I54] REVERSIBLE SPRAG CLUTCH 8 Claims,4 Drawing Figs.

I51] Int. Cl Fl6d 41/08 [50] Field of Search 192/41 A,

43, 43.1, 45.1; 188/822, 82.8; til/63.1, 62, 59.1

[56] References Cited UNITED STATES PATENTS 2,404,092 7/1946 Reynolds192/451 2,707,540 5/1955 Morris 192/451 2,981,389 4/1961 Kilness192/43.1 X 3,233,481 2/1966 Bacon 81/63 3,372,612 3/1968 Rozmus 81/62Primary ExaminerAllan D. l-lerrmann An0mey-Fryer,'Tjensvold, Feix,Phillips 8L Lempio ABSTRACT: A reversible sprag clutch has a pluralityof sprags disposed between spaced, opposed circular surfaces of twoconcentric members forming races for convex-convex contact wherein eachof the sprags has two distinct inner cam surfaces, one of which innercam surfaces can be employed to prevent relative clockwise rotationbetween the concentric members and the other of which inner cam surfacescan be employed to prevent counterclockwise rotation of the concentricmembers. These sprags are so constructed that the clutch transmittingtorque in one direction will allow unrestricted rotation in the oppositedirection depending upon which of the inner cam surface is cooperatingwith the inner race. Through the use of a selector ring to bias theindividual sprags, it is possible. to selectively reverse the directionof torque transmission to the clutch and allow freewheeling" in theopposite direction.

PATENW Am; a 7 m1 SHEET 1 OF 2 FIG..1

FlG 2 INVENTOR. DAVID N. SEDERQUIST FlG 3 ATTORNEYS PATENTEDAUGITIBYI34599767 sum 2 [1F 2 FIG 4 ENTO DAVID N. ERQU REVERSIBLE SPRAG CLUTCHBACKGROUND OF THE INVENTION other in one rotational direction but willgrip or lock these concentric parts as a unit instantaneously when thedirection of rotation is reversed.

Most common of these types of rudimentary clutches are those employing aplurality of rollers or balls contained in an opening between twoassociated concentric members wherein one of the opposed surfacesincludes a plurality of ramp surfaces cooperating with the rollers orballs. If the relative rotation between the concentric parts isattempted in one direction, the rollers or balls will roll up the rampand wedge between the surfaces locking or coupling the members togetheras a unit. However, if the relative rotation is reversed the rollers orballs will not be driven into wedging engagement between the adjacentsurfaces and therefore rotation of the members relative to one anotherin this direction can be freely accomplished.

Spray clutches, which are a variation of the roller or ball clutchespreviously described, include cam surfaces on a sprag member which willeffect the wedging action in one direction but not in the other.Depending upon a number of mechanical parameters, the design of thesesprags will vary in order to meet the particular torque requirements ina specific machine or device.

A common distinguishing feature of these rudimentary clutches is thatthey only allow unidirectional torque transmission and therefore areunsuitable where the direction of torque transmission may selectivelychange from one rotational direction to the other. Under such situationsthe prior art sprag clutches could not be employed without removing themfrom their connection and reversing them so that the inputs and outputswould be reversed relative to their connection in the machine. Such anoperation is both time consuming and laborious.

The primary objective of the instant invention is a provision of a novelselectively reversible sprag clutch which the direction of torquetransmission to the clutch can be conveniently and simply reversed.

Another object is the provision of the selectively reversible spragclutch which can be produced as economically as unidirectional sprayclutches.

It is also an object of the current invention to provide a reversiblesprag clutch which is small and compact and does no require a largenumber of parts for its reversing feature.

SUMMARY OF THE INVENTION The above objects and advantages can beaccomplished with a selectively reversible sprag clutch which includesan inner cylindrical member having a peripheral circular surface formingan inner race, an outer concentric ring member surrounding said innercylindrical member in a spaced relationship to provide annular spacetherebetween with an opposed circular surface forming an outer race, anda plurality of sprags circumferentially disposed in the annular spacebetween the inner and outer races with each of said sprags having anarcuate outer cam surface and two distinct inner arcuate cam surfaceswhereby the outer cam surface can cooperate with one of the inner camsurfaces to transmit torque in a clockwise direction and can alsocooperate with the other inner cam surface to transmit torque in acounterclockwise direction. The sprags are commonly biased in a circulardirection to achieve appropriate interaction of the respective pairs ofcam surfaces so that the direction of torque interchanged between thetwo respective concentric members can be selected.

BRIEF DESCRIPTION OF THE DRAWING The current invention will be betterunderstood from the following detailed description of a preferredembodiment read in conjunction with the attached drawings in which:

FIG. 1 is a perspective view of the selective reversible sprag clutchwith parts broken away to illustrate its construction;

FIG. 2 is an elevation shown in section of the sprag clutch illustratedin FIG. 1;

FIG. 3 is an end elevation of a sprag showing a torquereversing spring;and

FIG. 4 is an end elevation of one of the sprag members showing thedevelopment of its cam surfaces and the interaction of these surfaceswith the inner race and the outer race through control of which thetransmission of torque through the clutch can be selectively changed.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2 ofthe drawings, the design and details of the selectively reversible spragclutch 9 are illustrated. It consists of an inner cylindrical member 10having a peripheral circular race 11 and a concentric outer ring member12 which are journaled together with needle bearings 13 so the innercylindrical member and the outer ring member are free to rotate relativeto one another about a common axis. In the embodiment illustrated, theinner cylindrical member includes a female spline 14 which accepts oneof the spline shafts of the machine and the outer ring member has asimilar female spline 15 which accepts another shaft of the machinebetween which shafts torque interchange is selectively desired inalternate directions while allowing declutching in the oppositedirection.

The outer ring member 12 includes an internal circular race 16 which isdisposed in a radial registry around the circular inner race 11 of theinner cylindrical member 10 as illustrated in FIGS. 1 and 2, therebyforming an annular opening or space between these two circular races.Torque interchange between the respective members is accomplished byinserting a plurality of sprag means 17 between the spaced apartconcentric races which will wedge only when relative rotation betweenthe concentric members is attempted in one direction but hot when thedirection is reversed when biased one way and provide the reverseoperation when the bias is reversed. By biasing inner ends of the spragmeans in a common circular direction or reversing the direction of thebias, the direction of torque transmissions through the clutch can beselectively reversed. Further, by circumferentially disposing aplurality of the sprag means in the annular space between concentricraces, the radial forces developed by the wedging actions of theindividual sprag members will be offset by those developed by adiametrically disposed sprag means which allows the inner and outerraces to maintain concentricity during torque interchange between therespective cylindrical members of the clutch.

In the embodiment illustrated in FIG. 2, a shoulder 18 on the innercylindrical member 10 abuts on a surface of the outer ring member 12adjacent to the needle bearing 13 and a snapring 19 on the oppositesides of the needle hearing locks these two concentric members againstaxial movement. Through the needle bearing, the several parts of theclutch can rotate relative to one another about a common axis. Acircular flange 20 carrying the female spline 15 is attached to theouter ring member 12 with bolts 21. It should be appreciated that theillustration of the clutch in the drawings is a veryelementary-embodiment and is not designed to accept very large Theconstruction and principle cam contours of each of the individual spragmeans 17 is best illustrated in FIG. 4. It should be appreciated thatthe axial length of these sprag means can vary depending upon the torqueparameters to be transmitted in the clutch system. Of course, in theinstant reversible sprag clutch, torque capacity is limited by the hertzstresses, as it is in prior art sprag clutch designs, wherein the torquecarried by the clutch is equal to the sum of the tangential loadscarried by each sprag times the moment arm of each sprag. See AutomotiveSprag ClutchesDesign and Application by E. A. Ferris S.A.E. Library 208p. 12, June, 1960.

For the purposes of illustration, each sprag means 17 is equipped withcentral stepped pins 22 adjacent their outer cam surface as best shownin FIGS. 1 and 2. These stepped pins are received in circumferentiallyspaced bores in phasing rings or cages 23 on opposite sides of thesprags and are retained with snap rings 24 on outboard ends of thestepped pins. This illustrates one simple type of phasing ring or cagewhich can be employed to maintain the proper circumferential spacingbetween the tops of the individual sprag means for uniform torque loaddistribution.

Biasing of each of the sprag means for reversing the clutch isaccomplished by a plurality of U-shaped springs 25 best shown in FIG. 3mounted on a selector ring 26 which is mounted on the front phasing ringor cage so that it can be turned between two positions, F and R. Turningthe selector ring will cause one or the other leg of the U-shapedsprings carried on supports 26a extending through slots 23a in the frontphasing cage to engage a projecting stop 27 on the outer radial face endofits associated sprag means, as illustrated in FIGS. 1 and 2, throughwhich contact the contacting spring leg will urge the bottom end of itsassociated sprag means to cause one of the inner cam surfaces of thesprag means to come into contact with the inner race 11 as the spragmeans rotates about the axis of its stepped pins 22 in the phasing ringor cage. A setscrew 26b locks the selector ring to the phasing cage inone of its two positions.

Thus, by twisting the selector ring 26 on the phasing ring or cage eachof the U-shaped springs will bias its associated sprag means in a commondirection to select the direction of torque transmission through thereversible sprag clutch. After the sprag means are secured in thephasing ring or cages, this assembled unit is inserted in the annularopening A so that the inner edges of the sprag means abut on radialshoulder 18 and thereafter a snap ring 28 is employed on the inner race11 against the front faces of the sprag means retaining them between thesnapring and the shoulder 18 to prevent axial movement of this assembledunit.

By referring to FIG. 4, the actual development of the outer cam surface30 and the inner cam surfaces 31 and 32 are better illustrated whereinthe sprag means 17 biased in the direction of the arrow B so thatrelative rotation of the inner race 11 to the outer race 16 in thedirection of arrow C cannot occur due to the wedging action or cammingof the sprag means between the outer and inner races 16 and 11,respectively. However, since the inner cam surface 31 has a decreasinglever arm or strut from its drive point 33 (contact with the inner race)to the centerline 35 of the sprag means, a reversal of direction,opposite to arrow C, will not result in any wedging action when the biason the sprag means in the direction of the arrow B is maintained. As aresult, freewheeling can occur in this latter, counterclockwise,direction. Of course, if the sprag is rotated about pins 22 so that itsother inner cam surface 32 is biased toward inner race 11 by the U-shaped spring, the direction of torque transmission will be reversed andfreewheeling will occur in the opposite or clockwise direction since theoperation is the same due to the symmetry of the sprag means on oppositesides of their centerlines. Since the reversing torque through theclutch can be simply accomplished, the clutch is ideally suited forreplacing ratchet drives in socket tools where it is desirable to reducethe lost motion in a reversible drive.

More specifically, the basic geometry sprag design requires inner andouter cam surfaces of a sprag be developed from two spaced aparteccentric radii with the so-called horizontal eccentricity being themost important single dimension. If two lines D and E are drawn fromrotational axis of the two races through the center of the several radiidetermining the active inner and outer cam surfaces, it determines thecontact points of the cam surfaces with the several races. If a line isdrawn between these two contact points, it can be considered a strut S.Relative movement between the inner and outer races will cause the spragto rotate, toward an increasing or decreasing strut length. The raceswill lock if toward an increasing strut length and freewheel if toward adecreasing strut length. Through the novel design of the instantinvention, two inner active cam surfaces are provided which can bealternately employed.

Referring to FIG. 4, it can be seen that the sprag means 17 includes twosymmetrical halves on opposite sides ofa centerline 35, one of which isreversed or a mirror image of the other. As a result, the outer camsurface 30 may be developed by a single are having a center 36 in themidportion of the sprag means. One inner cam surface 31 developed by anare having its center at point 37 and the other inner cam surface 32developed by an are having its center at mint 38. It should be noted thecenter points of the arcs forming the inner cam surfaces 31 and 32respectively are offset (horizontal eccentricity) from the centerline sothat a common intersection point between the inner arcs will be oncenterline 35. Thus, the strut of each inner can surface will decreaseas frictional drag urges it toward the centerline of the sprag meansallowing freewheeling." The actual design and curvature of therespective cam surfaces can vary considerably and are not limited to thespecific design shown. More sophisticated sprags will include othercompensating radii selections which can be selected to meet designparameters required for the specific application.

What I claim is:

l. A selectively reversible sprag device comprising:

a first member having a race;

a second member supported in spaced relationship from said first memberand having an opposed race;

a plurality of sprag means between said race and said opposed race, eachof said sprag members having a single arcuate cam surface at one end andtwo arcuate cam surfaces at their opposite end with said two arcuate camsurfaces having horizontal eccentricity with respect to said singlearcuate cam surface at said one end; and

biasing means operably associated with said plurality sprag means tourge them selectively in one of two common directions whereby saidsingle arcuate cam surface of each sprag means and one of its twoarcuate cam surfaces at its opposite end will restrict relative movementof said first and second member in one direction and said single arcuatecam surface of each sprag means and the other of its two arcuate camsurfaces at its opposite end will restrict relative movement of saidfirst and second members in the opposite direction depending on thedirection of biasing means.

2. A selectively reversible sprag clutch comprising:

a first member having an inner circular race;

a second member rotatably journaled with said first member for rotationabout a common concentric axis, said outer member having an outercircular race disposed in radial registry with said inner circular raceand in a spaced relationship forming an annular opening between saidconcentric races;

a plurality of sprag means circumferentially disposed in said annularopening, each of said sprag means having an outer arcuate cam surfaceand two inner arcuate cam surfaces, each of said inner cam surfaceshaving horizontal eccentricity with their outer arcuate cam surface; and

biasing means selectively engaging said plurality of sprag means andurging them in one of two common directions, whereby a common innerarcuate cam of every sprag means cooperates with its outer cam surfaceto effect torque interchange between said first and second memberthrough said races in one rotational direction and the op posite innerarcuate cam surface of every sprag means cooperates with its outer camsurface to efiect torque interchange between said first and secondmembers in an opposite rotational direction depending on the directionof bias of said biasing means.

3. A selectively reversible sprag clutch as defined in claim 2 whereinthe plurality of sprag means are arranged so each sprag means iscomplemented by a diametrically positioned sprag means.

4. A selectively reversible sprag clutch as defined in claim 2 whereincage means are associated with the plurality of sprag means to maintainthem at equally spaced circumferential intervals in the annular openingbetween the concentric races.

5. A selectively reversible sprag clutch as defined in claim 4 whereinthe cage means includes an associated selector means operable toselectively change the direction of bias of the biasing means.

6. A selectively reversible sprag clutch as defined in claim 2 I

1. A selectively reversible sprag device comprising: a first memberhaving a race; a second member supported in spaced relationship fromsaid first member and having an opposed race; a plurality of sprag meansbetweEn said race and said opposed race, each of said sprag membershaving a single arcuate cam surface at one end and two arcuate camsurfaces at their opposite end with said two arcuate cam surfaces havinghorizontal eccentricity with respect to said single arcuate cam surfaceat said one end; and biasing means operably associated with saidplurality sprag means to urge them selectively in one of two commondirections whereby said single arcuate cam surface of each sprag meansand one of its two arcuate cam surfaces at its opposite end willrestrict relative movement of said first and second member in onedirection and said single arcuate cam surface of each sprag means andthe other of its two arcuate cam surfaces at its opposite end willrestrict relative movement of said first and second members in theopposite direction depending on the direction of biasing means.
 2. Aselectively reversible sprag clutch comprising: a first member having aninner circular race; a second member rotatably journaled with said firstmember for rotation about a common concentric axis, said outer memberhaving an outer circular race disposed in radial registry with saidinner circular race and in a spaced relationship forming an annularopening between said concentric races; a plurality of sprag meanscircumferentially disposed in said annular opening, each of said spragmeans having an outer arcuate cam surface and two inner arcuate camsurfaces, each of said inner cam surfaces having horizontal eccentricitywith their outer arcuate cam surface; and biasing means selectivelyengaging said plurality of sprag means and urging them in one of twocommon directions, whereby a common inner arcuate cam of every spragmeans cooperates with its outer cam surface to effect torque interchangebetween said first and second member through said races in onerotational direction and the opposite inner arcuate cam surface of everysprag means cooperates with its outer cam surface to effect torqueinterchange between said first and second members in an oppositerotational direction depending on the direction of bias of said biasingmeans.
 3. A selectively reversible sprag clutch as defined in claim 2wherein the plurality of sprag means are arranged so each sprag means iscomplemented by a diametrically positioned sprag means.
 4. A selectivelyreversible sprag clutch as defined in claim 2 wherein cage means areassociated with the plurality of sprag means to maintain them at equallyspaced circumferential intervals in the annular opening between theconcentric races.
 5. A selectively reversible sprag clutch as defined inclaim 4 wherein the cage means includes an associated selector meansoperable to selectively change the direction of bias of the biasingmeans.
 6. A selectively reversible sprag clutch as defined in claim 2wherein each sprag means is semisymmetrical with one of its two innerarcuate cam surfaces being a mirror image of the other.
 7. A selectivelyreversible sprag clutch as defined in claim 5 wherein springs associatedwith each sprag means and the selector means form part of the biasingmeans.
 8. A selectively reversible sprag clutch as defined in claim 2wherein the first member includes coupling means for coupling it to afirst shaft and the second member includes coupling means for connectingit to a second shaft coaxial with said first shaft.